[TA-3947]: add ledger_entry request

Description

This PR aims to add the missing ledger_entry request.

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Refactoring

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code where needed
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective
• New and existing unit tests pass locally with my changes

Changes

• New ledger.EntryRequest and ledger.EntryResponse

Notes

ledger_entry request seems to not be valid when running it on xrpl.js. Await to a fix in order to merge and release this feature